The imaging of body surfaces through an endoscope is well known within the medical and veterinarian fields. Typically, this involves inserting an endoscope into a body cavity and directing a high intensity light source output through the endoscope to illuminate body tissue. Light reflected by the body tissue then is guided along an optical path to an image sensor to generate both video and still images of the tissue. One such approach is described in U.S. Pat. No. 5,162,913 to Chatenever et al., and provides a technique for an automatic adjustment of the exposure of video images detected with a CCD (charge coupled device) image sensor.
The use of high intensity light sources involves potential hazards to medical personnel and patients. For example, when a light guide cable, used to convey the high intensity-light source output, is momentarily disconnected from the endoscope and placed on a sterile drape used to protect the patient, the high intensity of light output can be sufficient to ignite the drape and pose a fire hazard; or, the user can inadvertently hold the disconnected light guide cable in such a way as to temporarily blind another person in the room. In some instances, when the endoscope is removed from (i.e., pulled out of) a patient, there can be a risk of these same hazards. When the light source is used with an endoscopic video camera, which has an automatic exposure system, the light source output intensity may be turned up to a intensity level higher than required for the camera to produce well-exposed images. This increased light intensity level can desiccate body tissue and cause serious injury to the patient. Typically, endoscopic video camera automatic exposure systems can produce well-exposed images with an electronic shutter setting of approximately 1/125th to 1/500th of a second. If the distal end of an endoscope is placed within close proximity to tissue being imaged, typically, a relatively lower light intensity level will still enable an endoscopic video camera to produce well-exposed images. An undesirable, and potentially dangerous, scenario can occur if the light source output is set to a high intensity level, and the endoscope distal end is placed within close proximity to tissue being imaged. Typically, in such a case, automatic camera exposure systems will adjust the electronic shutter setting to approximately 1/10,000th of a second (or faster) to compensate for the high illumination reflections from the tissue. In such a situation, the risk of desiccating delicate tissue is greatly increased.
Thus, it is desirable to solve these problems, specifically to control the output from a high intensity light source so that the light source intensity is automatically reduced to a safe level when the light source output is not directed to a surface and/or the camera/imager or light-guide are disconnected from each other. It is also desirable to protect tissues operated on during a surgical procedure from overheating or burning due to the intensity of the light source being set higher than required to produce well-exposed images. It is also desirable to protect the eyes of the operator of an endoscope or persons in the surgical area from direct exposure to high intensity light used in medical devices such as endoscopes and the like.
Techniques for controlling the output intensity from a light source are known in the art. For example, a technique for automatically controlling the light intensity from a light source, on the basis of an image signal from an imaging unit associated with an endoscope, is described in Japanese Unexamined Patent Publication No. 62-155689 as mentioned at column 2, lines 1-21 in U.S. Pat. No. 5,957,834 to A. Mochida. As recognized in the Mochida patent, when light intensity control is made dependent upon a signal derived from the image, then upon removal of the endoscope from the body, the control is likely to increase the output intensity level from the light source, when instead it should decrease the output to protect the operator's eyes from inadvertent high intensity light exposure and prevent ignition of combustible material. In the Mochida patent, a switch is added to manually adjust and control the output of the light source when the endoscope is removed from a body.
As further described in the Mochida patent, the output intensity level of the light source is controlled by regulating the position of a diaphragm with respect to the light source. The control signal for doing this is derived from an image sensor in the endoscope.
In U.S. Pat. No. 4,527,552 a photoelectric element generates a signal indicative of the intensity of light reflected from an object illuminated by a light source associated with the endoscope to control the light source output level. In U.S. Pat. No. 5,131,381 a light source associated with an endoscope is controlled by a signal that represents the density value of each line of a camera video image derived through the endoscope. Other patents relevant to light intensity level controls for endoscopes are U.S. Pat. Nos. 3,670,722; 4,963,960; 4,561,429; 5,091,779; 5,134,469; 5,159,380; 6,767,320; 7,070,560; 7,585,276; 7,798,959; 7,847,817; and 7,828,726.
Techniques have been proposed to reduce the risks associated with high intensity light sources. One involves a special light guide cable with wires in it that are shorted together when the cable is attached to an endoscope. The short is detected at the light source and light output intensity is reduced when the cable is disconnected and the short is subsequently removed. A retractable mechanical shroud, which covers the light guide cable end when not connected to an endoscope, has also been suggested.
These safety solutions are not necessarily effective against all potential hazardous conditions that may arise; such as when the endoscope with the light guide cable still attached is pulled out of a patient and inadvertently directed at a person or surgical drape, or when the light guide or source initially is directed to treat openly accessible tissue and inadvertently misdirected during or after a procedure, or when a video camera head, attached to the endoscope light guide cable combination, is disconnected from its corresponding control unit.
One such approach to solve this problem is described in U.S. Pat. No. 6,511,422 to Chatenever (hereinafter Chatenever '422). Chatenever '422, herein incorporated by reference, describes a method and apparatus where the output from a high intensity light source is controlled so that whenever the output is not directed at tissue (meaning that the endoscope/video camera/light source combination is not currently being used to image body tissue), the light source output intensity is automatically reduced to a safer level. This is done by monitoring the reflected light from tissue and when this reflection indicates that the light source is not directed at tissue, the light intensity is turned down to a safer level. This involves generating a modulation signal and modulating the intensity of the light source output with the modulation signal.
Chatenever '422 involves monitoring the light reflected by a surface, detecting the modulation in the monitored light, and reducing the intensity of the light source output when the detected modulation is below a reference level. However, Chatenever '422, while effective as a safety solution, has problems controlling Xenon lights and other light sources because the amplitude or frequency modulation methods described by Chatenever '422 do not work well with light sources having these problems. Specifically, Chatenever '422 does not work well with lights sources that have slow-response, high-frequency noise, nonlinearity, and non-monotonic response times, such as Xenon lights. It is thus desirable to provide an improved method and apparatus that works with light sources that have slow-response, high-frequency noise, nonlinearity, and non-monotonic response times.
It is also desirable to improve upon the methods and apparatus described in the Chatenever '422 patent to overcome problems to control Xenon light sources, as Xenon light sources have increased applicability in endoscope technology. None of the other existing methods and apparatuses described in the prior art work effectively with light sources that have slow-response, high-frequency noise, nonlinearity, and non-monotonic response times.
It is further desirable to provide a method and apparatus to upgrade existing and future endoscopic imaging systems with a light source control (“LSC”) feature that solves problems associated with light sources, such as Xenon lights. It is also desirable to do so in a cost effective way, and without any hardware change in product lines of light sources and endoscopic imaging systems.
It is also desirable to design a cost-effective single LSC implementation based on the method that is suitable for various existing and yet to be developed product lines of light sources, camera heads, camera control units (“CCUs”), videoscopes, and endoscopes. It is also desirable to provide software that executes upon hardware.
It is also desirable to provide a method and apparatus for LSC that enables adaptive normalization and self-calibration; so as to simplify the adjustment of the LSC feature to new endoscopic imaging systems and light sources and to minimize manual adjustment.
It is also desirable to provide a self-recovery method that involves the adaptive normalization and self-calibration techniques, so as to recover and/or optimize the LSC feature to possible new vs. replacement of light source and/or the type of the scope attached to the camera during surgery, and/or the camera type of CCU during use and/or surgery.